Electrical sound reproducing apparatus



July 9, 1946. c, WARNER 2,403,696

ELECTRICAL SOUND REPRODUCING APPARATUS Filed Aug. 14, 1944 IN VEN TOR.

HARRY C. WARNER. BY

(/ f a I ATTORNEY.

Patented July 9, 1946 r ELECTRICAL SOUND REPRODUCING APPARATUS Harry C.Warner, San Francisco, Calif.

Application August 14, 1944, Serial No. 549,379

My present invention relates to electrical sound reproducing apparatus,and more particularly to a device for providing a modulated input signalcurrent for a vacuum tube amplifying system.

An object of the invention is to provide anew and novel form of currentmodulating device which is particularly adapted to operate inconjunction with a sound responsive device, such as a phonograph pick-upor microphone, to provide an input signal current for a vacuum tubeamplifier circuit.

Another object of the invention is to provide a current modulatingdevice of the resistance typ in which the resistance of a liquidconducting medium may be varied in a new and novel manner to provide asignal current for the input of a vacuum tube amplifying system.

A further object of the invention is to provide a phonograph pick-updevice of novel construction for use with a vacuum tube amplifyingsystem of the type employed to reproduce the recording upon a soundrecord.

Other objects and advantages of the invention will be in part evident tothose skilled in the art, and in part pointed out hereinafter in thefollowing description taken in connection with the accompanying drawing,wherein there is shown by way of illustration and not of limitation,preferred embodiments of the invention.

In the drawing;

Figure 1 is a. substantially normal-size view of the invention asembodied in a pick-up for the tone arm of a phonograph,

Figure 2 is an enlarged sectional view with parts broken away andshowing details of construction of a preferred embodiment of a featureof the invention,

Figure 3 is a transverse sectional view taken along line IIIIII ofFigure 2,

Figure 4 is a diagrammatic wiring diagram showing a system ofconnections by which my device may be associated with the input of avacuum tube amplifying circuit, and

Figures 5 and 6 are diagrammatic views showing other adaptations of theinvention.

In Figure 1 of the drawing, for the purpose of illustration, I haveshown my invention as embodied in a pick-up device, such as may be usedto electrically reproduce the recorded program upon a sound record. Inthis showing the numeral I0 designates a supporting housing ofinsulating material, such as is now generally used as a mounting for apiezo-electric crystal of a phonograph pick-up device. i'his housing 10is constructed in two substantially symmetrical 8 Claims. (Cl.179-10041) parts between which terminals H and I2 extend from one endfor connection with a vacuum tube amplifier circuit. At their other endthe halves of the housing H) are provided with diagonally disposed andregistering half-round grooves l3 that will provide a cylindrical seatfor two relatively soft rubber collars l4 and i5 within which a recordneedle supporting member I6 is pivotally mounted. Carried by the memberii there is a suitable thumbscrew I! by means of which a needle [8 maybe secured within the support It. Extending inwardly, and also carriedby the support It, there is an operating arm l9 that is adapted tocontrol a variable'resistance device 20 which embodies what are nowconsidered to be the novel aspects of my present invention. As hereshown, the variable resistance device 20 is in the form of a smallcapsule which is positioned within a recess 2| formed in one side of thehousing l0 so that its axis will be approximately in line with aprojection of the axis of the record engaging needle I 8. As willhereinafter appear, the device 20 is believed to operate on theprinciple of a variable resistance and it is here shown as beingconnected at its ends through conductors 22 and 23 to the terminals IIand I2 which in turn are adapted to connect with the input terminals ofa vacuum tube amplifier circuit.

Reference is now made to Figures 2 and 3 of the drawing for a moredetailed description of the invention as embodied in a device suitablefor use as above indicated. In these figures the device 20 illustratedin Figure 1 is shown on a greatly enlarged scale. As at presentconstructed, the unit or capsule has a diameter of approximately seventhirty-seconds of an inch and an overall length of one-half inch, andthe amount of liquid required as a variable resistance medium, as willhereinafter appear, amounts to approximately two full drops. In itspreferred form the device 20 comprises a length of relatively softrubber tubing 24 that is adapted to-be closed at its ends by means ofelectrodes 25 and 26 that project into the ends thereof so as to form anair-tight liquid containing chamber 21 therebetwcen which is adapted tobe filled with a liquid resistance medium. As here shown, the electrodes25 and 26 are each provided with an annular recess 28 into which theends of the tubing 24 are clamped by means of suitable binding rings 29.Extending between the electrodes 25 and 26 there is a spacing member 30of insulating material which is seated at its ends within the electrodes25 and 26 in such a manner that they will be held in properly spacedrelation with respect to each other. This spacing member 30 has anannular collar or enlargement ll intermediate its ends which ischamiered so as to provide for a substantially knife edge engagementthereof with the inside wall of the tubing 24, and at one point aroundits circumference, as is more clearly shown in Figure 3 f the drawing,this annular collar or enlargement 3| is provided with a notch orcutaway portion 32 that serves to provide a constricted conductance pathin the liquid resistance medium contained within the chamber 21. As ismore clearly shown in this latter figure of the drawing, the rubbertubing 24 is adapted to be engaged on its outer surface, at a pointimmediately adjacent the notch or cut-away portion 32, by the operatingmember I9 previously referred to as actuated in accordance with themovements of the record engagin needle l8 when the latter is operatingupon a sound recording.

In Figure 4 of the drawing I have shown a diagrammatic circuit by meansof which my invention may be associated with a vacuum tube amplifiercircuit. At this point it should .be stated that while it is believedthat the operation of my improved device is based upon the principle ofa variable resistance as a modulating means, it is to be understood thatthis action may be accounted for by some other theory. The nature of theliquid resistance medium does not appear to be of major importance, butit has been found that grain alcohol or, in fact, ordinary whiskey, maybe used as a resistance medium between the electrodes 25 and 28. Thefact that an alcohol, as distinguished from an acid electrolyte, hasbeen found to be particularly effective in this instance, may be due toits inactivity with respect to the rubber tubing. There is also theknown fact that the alcohols have a high inductive capacitance value andit is, therefore, possible that the use of such a liquid resistancemedium may in some way involve a capacitive change in the circuitbetween the electrodes 25 and 26. In any event, it has been demonstratedby actual use that a device constructed as above described is capable ofproviding for the reproduction of recorded music in a much smoother andmore satisfactory manner than is possible with the best piezo-electriccrystals now on the market for this purpose. Among other advantages, ithas been found possible, by changing the resilience or thickness of thetubing 24, to provide for almost any desired frequency response. Forexample, a thin walled tubing has been found to be very responsive inthe higher frequency range, while in the lower frequency range theresponse is more pronounced as the thickness of the tubing 24 isincreased. Another point is that by changing the nature of the liquidand/or the length of the current path therethrough, it will be possibleto match the input impedance of any amplifier circuit with which thdevice may be used. And finally, it has also been discovered that theoperation of the device is not affected by changes in temperature orhumidity, which is a characteristic not possessed by the so-calledpiezo-electric crystal microphone and pick-up devices.

In operation, when the device 20 is associated with a vacuum tubeamplifier circuit, as diagrammatically shown in Figure 4 of the drawing,one of its electrodes, as for example, the electrode 25, will beconnected through a conductor 33, a coupling resistor 34 and a conductor35 to the positive side of the output or plate circuit of a vacuum tube38, which tube is here shown as having a control grid 31, a filament 38and a plate 39. This electrode 2,5 is also shown as connected through acapacitance 40 to the grid 3'! of the vacuum tube 38. At the other sideof the device 20 the electrode 28 is connected through a conductor 4| tothe grounded side of the filament 3| and through a grid leak resistance42 to the grid 31 of the vacuum tube 36. A plate coupling-rm sistance 43is also here shown as connected across the plate or output circuit ofthe vacuum tube 36. This output circuit also hasa blocking capacitance44 in one side thereof. When the device 20 is connected in this manner,it is believed that a current flow will be established through theconductor 35, the coupling resistance 34 and the conductor 33 to theelectrode 25, and from there through the variable resistance medium tothc electrode 25 and via the conductor H to ground at the point ofconnection with the filament ll of the vacuum tube 36. Now, with thiscurrent flowing through the variable resistance medium of the device 20,it will be seen that when the recording needle I! is stationary, nochange will occur in the nature of the conductance path be tween theelectrodes 25 and 26 and, therefore, a. substantially uniform flow ofcurrent will prevail. However, when the nature of the conductance pathformed by the resistance liquid medium in the constricted zone of thechamber 21 is varied, as by movements of the record engaging needle I8,it is believed that these changes will produce a modulation of thiscurrent which will then be transmitted through the condenser 40 and thegrid leak resistance 42 to the grid 31 of the vacuum tube 36, and inthis way the vacuum tube 36 will operate to produce an amplified signalcurrent that may be used to operate a loud speaker or other similardevice. It is also conceivable that the circuit through the variableresistance liquid medium of the device 20 may also be subjected to ahigh frequency carrier current originating in the plate circuit of thevacuum tube 35 upon which the modulated signal current may be.

superimposed.

While I have illustrated and described my invention as embodied in adevice for use in connection with the reproduction of phonographrecordings, it will be readily understood that the device 20 may befound useful in other fields. For example, as shown in Figure 5 of thedrawing, it may be used in connection with a sound wave responsivemicrophone by operating the device 20 in association with a sound waveintercepting diaparagm 45 or, as shown in Figure 6 of the drawing,wherein the device is illustrated as associated with a mechanicallyoperated detector device 46 that may be placed against any vibratingsurface for the purpose of reproducing electrical impulses correspondingto the movements of a vibrating member.

While I have, for the sake of clearness and in order to disclose theinvention so that the same can be readily understood, described andillustrated specific devices and arrangements, I desire to have itunderstood that the invention is not limited to the specific meansdisclosed, but may be embodied in other ways that will suggestthemselves to persons skilled in the art. It is believed that thisinvention is new and it is desired to claim it so that all such changesas come within the scope of the appended claims are to be considered aspart of this invention.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. In a phonograph pick-up of the character described, the combinationof a supporting housaeoacoc conductance path between said electrodes,and

means operated by movements of said stylus adapted to deform saidreceptacle and'thereby change the conductance of said liquid inaccordance with the recording upon a sound record.

. 2. In a phonograph pick-up of the character described, the combinationof an insulated supporting housing adapted to be carried by the tone armof a phonograph, a stylus pivotally mounted upon and extending from saidhousing adapted to engage a sound record, a tubular rubber receptaclehaving spaced electrodes closing the ends thereof and adapted to beconnected in the input circuit of a vacuum tube with the plate to groundpotential of said vacuum tube impressed therebetween, 'a liquid mediumwithin said receptacle forming a variable conductance path between saidelectrodes, and means operated by movements of said stylus adapted todeform said tubular receptacle between said electrodes to thereby varythe cross-section and conductance of said liquid between said electrodesin accordance with the recording upon a sound record.

3. In a control device for vacuum tube circuits, the combination of atubular non-metallic member having current conducting electrodes formingclosures at the ends thereof, a current conducting liquid forming aconductance path within said tubular member between said electrodes,means forming a constricted cross-section of said liquid. at a pointbetween said electrodes, and a sound wave responsive means adapted todeform the combination of an input tube having filament, grid and plateconnections, a variable resistance medium comprising spaced electrodeswith a column of conducting liquid therebetween, circuit connectionsbetween one of said electrodes and the plate and through a capacitanceto the grid of said vacuum tube, 'a circuit connection between the otherof said electrodesand the filament grounding circuit of said tube,whereby the plate potential of said tube will be impressed upon saidliquid through said electrodes, and mechanical means responsive to soundwave impulses adapted to vary the cross-section of said column ofconducting liquid between said electrodes, whereby .a modulated currentcorresponding to the response of said sound wave responsive means willbe impressed upon the grid of said input tube.

6. In a variable resistance unit for a current modulating device, thecombination of a pair of spaced electrodes, a tubular rubber sleevesecured at its ends around each of said electrodes and forming a liquidcontaining chamber therebetween, means between said electrodes operatingto divide said chamber into two parts with a restricted communicatingpassageway therebetween, a current conducting liquid disposed withinsaid chamber forming a variable resistance between said electrodes, andmeans including a sound wave responsive device adapted to distort thewall of said tubular sleeve adjacent said re stricted passageway,whereby the overall resistsaid tubular non-metallic member at the pointof said constriction to thereby change the overall conductance of saidliquid between said electrodes in accordance with sound wave impulses towhich said sound wave responsive means may be exposed.

4. In a sound wave control device for vacuum tube circuits, thecombination of a grid controlled vacuum tube, a receptacle havingopposed and insulated electrodes mounted therein and adapted to beconnected through a capacitance in the grid circuit of said vacuum tube,connections whereby the plate'potential of said vacuum tube is impressedacross the space between said electrodes, a liquid current conductingmedium disposed between said electrodes, means located between saidelectrodes forming a restricted current path in said liquid, andmechanical means responsive to sound wave impulses adapted to vary thecross-section of the restricted current path in said liquid inaccordance with the nature or sound wave impulses to which saidmechanical means is exposed.

ance of said liquid conducting rnedium will be changed in accordancewith the operation oi said means. I

7. In a control device for vacuum tube circuits, the combination of acapsule-like unit comprising an elongated yielding body portion ofinsulating material having current conducting electrodes sealed in andclosing the ends thereof to provide a fluid containing cavity, a fluidmedium disposed within said capsule and forming a current conductingpath between said electrodes, and means associated with the yieldingbody portion of said capsule adapted to exert a deforming pressurethereupon, whereby the conductance of the current path through saidfluid medium 5. In a sound reproducing vacuum tube circuit.

between the electrodes at the ends of said capsule will be varied inaccordance with the operations of said means.

8. In a control device for vacuum tube circuits, the combination of acapsule-like unit having a yielding body portion of insulating material,current conducting electrodes sealed in the wall of said capsule andforming therewith a closed fluid containing cavity, a fluid mediumdisposed within said capsule between said electrodes and forming acurrent conducting path therebetween, and means associated with theyielding body portion of said capsule adapted to exert a deformingpressure thereupon, whereby the conductance of the current path throughsaid fluid between said electrodes will be varied in accordance with theoperations of said means.

HARRY C. WARNER.

